With the development of Internet, a BRAS (Broadband Remote Access Server) or a BNG (Broadband Network Gateway) needs to gradually enhance various value-added service processing capabilities, for example, OTT (Over the top) video processing, DPI (Deep Packet Inspection), a firewall, and antivirus. Currently, expansion of all those capabilities is concentrated on the BRAS or the BNG. However, because there will be more types of value-added services in the future, when each service is expanded, software upgrade and even hardware upgrade need to be performed on the BRAS or the BNG. Regardless of the software upgrade or the hardware upgrade, an operator needs to power off a BRAS or BNG device, and original services of users on the BRAS or the BNG are interrupted. Currently, the number of users that the BRAS or the BNG can support is very large, and if device power-off is performed, the range of influence from the power interruption can be very large, which greatly affects user experience.